1. Field of the Invention
The present invention relates to a switch for controlling a circuit, more particularly to a switch, which has an overload release structure such that in case an overload current flows through the switch in a switch-on position, an alloy plate will be displaced from its initial position because an overload current flows through the switch in a switch-on position so as to prevent the switch from being damaged.
2. The Prior Arts
A conventional switch generally includes a button movable between a switch-on position, where a looped circuit is resulted in the switch so as to permit current flows therethrough, and a switch-off position, where an open circuit is resulted in the switch so that current will not flow therethrough. A majority of the switches presently available are provided with overload release structures, such as by installing fuses or circuit breakers, so as to prevent the switches from being damaged when an overload current flows therethrough.
There are plenty of patents regarding the switches provided with overload release structures. The applicant possesses U.S. Pat. No. 5,262,748 concerning a switch with overload release structure. Some U.S. Pat. Nos. 4,167,720; 4,937,548; 5,223,813; 5,451,729 and 5,558,211 respectively disclose a switch with overload release structure.
A conventional switch with an automatic overload release structure includes a switch casing defining an interior chamber, conductive first, second, third prongs disposed within the interior chamber and having lower prong sections exposed from the switch casing such that the lower prong sections of the first and second prongs are used for electrically connection with the fire and neutral wires of an electrical power source while the lower prong section of the third prong is used for grounding or earthing, wherein the upper prong section of the first prong is provided with a lower electrical contact while the upper prong section of the second prong is connected securely to one end of a heat-deformable alloy plate disposed within the interior chamber. The alloy plate further has a free end provided with an upper electrical contact in alignment with the lower electrical contact. A button is mounted pivotally on the switch casing, includes a connection rod having a barbed lower end operably connected to the free end of the alloy plate. In addition, an elastic member is used for biasing the free end of the alloy plate for retaining the initial position of the alloy plate.
Pressing downward of a first end of the button with respect to the switch casing results in simultaneous downward movement of the connection rod, thereby causing touching between the lower and upper electrical contacts, where a looped circuit is formed between the first and second prongs via the alloy plate such that the button is disposed in a switch-on position. It is to note that the elastic member deforms during touching between the upper and lower electrical contacts until the elastic member retrieves the initial shape or position so as to retain the alloy plate at the initial position.
Pressing downward of a second end of the button with respect to the switch casing results in simultaneous upward movement of the connection rod together with the alloy plate, thereby causing separation between the upper and lower electrical contacts against the biasing action of the elastic member, where an open circuit is formed between the first and second prongs such that the button is disposed in a switch-off position. It is to note that the elastic member deforms during separation between the upper and lower electrical contacts until the elastic member retrieves the initial shape or position so as to retain the alloy plate at the initial position.
One drawback of the above-mentioned switch resides in that in case an overload current flows therethrough and thus results in an overheated situation, the alloy plate deforms due to the temperature of the overheat exceeds the predetermined deformation temperature of the alloy plate. During the deformation, the free end of the alloy plate will deform tremendously and buckles upward, thereby forming an open circuit between the upper and lower electrical contacts. In the same manner, the elastic member deforms simultaneously with the alloy plate until the upper and lower contacts at the free end retrieve to their respective initial position, where the elastic member retains the alloy plate at its initial position.
It is noted that the above-mentioned elastic member is in the form of a leaf spring and hence has a relatively large flexibility, which, in turn, influences the relative movement of the free end of the alloy plate with respect to the conductive first and second prongs, and hence the final precise position of the free end of the alloy plate.